this one of these movies that makes it fukking point
shyt was so damn confusing to us common brehs... you can see exactly how everyone got fukked over... dude on reddit, combined with a few posts in here, is as close as you can get to it.....
It's not that confusing and you could've basically summed it up like this:
Think of mortgaged back securities or CDO's as a house.
People like Burry took out insurance on that house betting that a tornado was going to come and destroy the house.
Since said house is made of steal and concrete, and never gets totaled, investment banks were like

ok.. we'll take those monthly insurance payments (because it was easy money to them).
But the house was actually made out of tooth picks and toilet paper.
Once the banks realized it, and saw the forecast called for thunderstorms tomorrow, they not only kept selling houses and lying saying they were made of steel, they also took out insurance as well
AIG sold insurance to everyone.. that's why it had to be bailed out.
The banks that collapse, got stuck holding assets (houses) as the tornado came and destroyed the houses that were still on their books (this is because they had to hold them on their books for a certain amount of time before they could sell them).
So at the end of they day, they took an investment that was reliable and made it unreliable all in the name of commissions.
Investment banks fukk over a lot of people including Pension funds, 401k's etc. because they all sold those instruments to them.